1. Field of Disclosure
The present disclosure relates generally to encoding of video signals, and more specifically to sub-pixel interpolation and its application in motion compensated encoding of a video signal.
2. Related Art
A video signal generally contains a sequence of video frames as is well known in the relevant arts. Each video frame may be represented as multiple pixels having corresponding pixel values, as is also well known in the relevant arts.
There is often a need to encode a video signal at one end and then decode the encoded signals at the other end. Encoding generally refers to converting pixel values of a frame according to an approach (encoding approach) such that the encoded data can be converted back to the original digital values within an acceptable error level. The reconversion is referred to as decoding.
An encoding technique entails predicting a frame and generating a difference from the predicted frame. The difference may be further compressed and sent as an encoded signal. A receiving system also attempts to predict the frame based on prior decoded frames and adds the differences to the locally predicted frame in decoding a received encoded signal.
Motion compensation is a technique employed to attain further compression in generating encoded signals. In general, a frame is logically divided into smaller blocks and a motion vector is generated representing the movement of a block sought to be encoded. The difference values noted above, are based on the blocks moved (of the locally predicted frame).
Assuming the movement is accurately predicted, the difference data would also require fewer bits to represent and thus further compression may be attained in the encoding operation. Thus, there has been a general need to predict the motion vectors accurately. The motion vectors are often specified in terms of pixel positions, and there has been a recognised need to predict the movement to the granularity of sub-pixels.
Supporting the sub-pixel motion estimation requires that the image frame also be generated at sub-pixel granularity, though the hardware (e.g., image sensors) may only generate pixels for each pixel position. That is, it is required that additional pixel values (corresponding to the sub-pixel positions) be generated from the source pixels generated by the sensor (or those generated after suitable further processing for the same positions).
Interpolation has often been used to generate sub-pixel values. Interpolation generally entails processing surrounding values to generate the sub-pixels sought to be computed. In general, it is desirable that interpolation be performed while meeting various criteria such as reduced resource requirements, reduced space on the silicon/wafer and/or reduced time, etc., as suited for the specific environment.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.